1. Field of the Invention
An aspect of the invention relates to a steering assist control apparatus and a steering assist control method.
2. Description of Related Art
In recent years, as an apparatus to support the driving of an automobile, there has been proposed an apparatus that performs the steering assist control to control the steering of an own vehicle, by giving a steering manipulated variable to a steering system of the own vehicle such that the own vehicle runs along a lane. For example, Japanese Patent Application Publication No. 2003-040132 (JP 2003-040132 A) discloses an apparatus including: running lane information detection means 31 for detecting a lane line that demarcates a lane; and control means 14 for keeping an own vehicle in the lane by giving a steering control torque to a steering system as a manipulated variable, based on the information detected by the running lane information detection means 31. In the apparatus of JP 2003-040132 A, when a detectable state in which the running lane information detection means 31 can detect the lane line is changed into an undetectable state, the control means 14 sets the steering control torque such that the behavior change of the own vehicle can be suppressed, gradually decreases the steering control torque, and stops giving the steering control torque to the steering system.
By the way, in the case of the occurrence of a recognition abnormality that makes it impossible to normally recognize the lane, if the manipulated variable for the steering assist control is gradually decreased in the same way in common with the above apparatus of JP 2003-040132 A, the steering assist control is stopped, regardless of the manner of the recognition abnormality, similarly to the case of the occurrence of an ordinary recognition abnormality. Therefore, there has been desired an apparatus that, at the time of the occurrence of an abnormality, can more adequately decrease the manipulated variable for the steering assist control, corresponding to the manner of the abnormality.
For example, in a manner of the recognition abnormality in which the lane line cannot be detected for only an extremely short time because of a partial absence of the lane line or the like, the abnormality is highly likely to be dissolved, and therefore, it is desired that the manipulated variable for the steering assist control is decreased to zero over a relatively long time. Meanwhile, in a manner of the recognition abnormality in which a lane line of a branched road along which the own vehicle is not running is falsely detected as a lane line of a lane along which the own vehicle is running, the steering of the own vehicle is likely to be controlled in an inadequate direction, and therefore, it is desired that the manipulated variable for the steering assist control is decreased in a relatively short time.